This invention relates to a new and improved system for injecting bursts or jets of air into a person's respiratory system to assist ventilation and respiration.
The mechanical application of positive pressure pulses of oxygen and air to a person's respiratory system has become fairly routine in neonatal, pediatric and adult intensive care facilities. With the more conventional ventilators, relatively large volumes of oxygen and air are applied to a person's respiratory system at frequencies which coincide generally with the normal inhalation frequency of the person. Another type of ventilator, known as a volume ventilator and typically used in adult and pediatric intensive care facilities, may operate in modes which apply the oxygen and air at fixed time intervals, or in modes that use respiratory effort to trigger the application of the oxygen and air.
Neonatal intensive care facilities typically use time-cycled, pressure-limited ventilators which provide a generally constant bias flow of fresh gas (oxygen and air) through a patient breathing circuit attached to the infant's respiratory system. FIG. 1 shows a pneumatic diagram of a typical prior art time-cycled, pressure-limited ventilator in which the pressure behind a diaphragm 2 in an exhalation valve 4 controls the pressure of gas in a tube 8, inserted into the infant's trachea. This diaphragm occludes the exit of exhaled gas from the patient breathing circuit shown in FIG. 1 until the pressure within the breathing circuit feed tube 8 exceeds the pressure behind the diaphragm 2, at which time gas is allowed to escape via discharge tube 12. Mechanical ventilation of the infant's respiratory system is provided by varying the exhalation valve 4 diaphragm pressure between a low value, called positive end-expiratory pressure (PEEP), and a high value, called the pressure limit. The ventilator of FIG. 1 cycles the application of gas to the infant at a fixed ventilation rate and for a fixed duration of time based on settings chosen by the operator. Attempts have been made to produce neonatal ventilators which trigger the delivery of gas to the infant based on respiratory effort, but because of difficulties in detection (in infants) and timely response, such attempts have generally proven unsuccessful. Still, it would be desirable to combine volume ventilators and neonatal time cycled/pressure limited ventilators into one unit so that the unit could be used either for pediatric intensive care or neonatal intensive care.
In addition to the conventional ventilator approach in which oxygen and air are applied to a person's respiratory system at frequencies generally coinciding with normal inhalation frequencies, it has been found that persons with various respiratory problems and illnesses can be benefited by the application of rapid, positive pressure pulses of oxygen and air to the persons' respiratory system. Examples of apparatus and methods of applying positive pressure pulses of gas to a patient at a higher than normal rate of inhalation and exhalation are disclosed in U.S. Pat. Nos. 4,481,944 and 4,538,604, and the references cited therein. Of course, such ventilators are not suitable for all respiratory problems and so if complete respiratory care is to be provided, both the rapid pulse ventilator and conventional ventilator would be necessary.